GNU Info

(libc.info)Binary Streams

---

Next: File Positioning Prev: Error Recovery Up: I/O on Streams

---

Enter node , (file) or (file)node

Text and Binary Streams
=======================

   The GNU system and other POSIX-compatible operating systems organize
all files as uniform sequences of characters.  However, some other
systems make a distinction between files containing text and files
containing binary data, and the input and output facilities of ISO C
provide for this distinction.  This section tells you how to write
programs portable to such systems.

   When you open a stream, you can specify either a "text stream" or a
"binary stream".  You indicate that you want a binary stream by
specifying the `b' modifier in the OPENTYPE argument to `fopen'; see
Note: Opening Streams.  Without this option, `fopen' opens the file
as a text stream.

   Text and binary streams differ in several ways:

   * The data read from a text stream is divided into "lines" which are
     terminated by newline (`'\n'') characters, while a binary stream is
     simply a long series of characters.  A text stream might on some
     systems fail to handle lines more than 254 characters long
     (including the terminating newline character).

   * On some systems, text files can contain only printing characters,
     horizontal tab characters, and newlines, and so text streams may
     not support other characters.  However, binary streams can handle
     any character value.

   * Space characters that are written immediately preceding a newline
     character in a text stream may disappear when the file is read in
     again.

   * More generally, there need not be a one-to-one mapping between
     characters that are read from or written to a text stream, and the
     characters in the actual file.

   Since a binary stream is always more capable and more predictable
than a text stream, you might wonder what purpose text streams serve.
Why not simply always use binary streams?  The answer is that on these
operating systems, text and binary streams use different file formats,
and the only way to read or write "an ordinary file of text" that can
work with other text-oriented programs is through a text stream.

   In the GNU library, and on all POSIX systems, there is no difference
between text streams and binary streams.  When you open a stream, you
get the same kind of stream regardless of whether you ask for binary.
This stream can handle any file content, and has none of the
restrictions that text streams sometimes have.